In multiple-input multiple-output (MIMO) communications systems, antennas may be used on both a base station and on a mobile device to exploit a phenomenon known as multipath propagation to achieve higher data rates. In general, MIMO communications systems simultaneously send and receive multiple data signals over each radio channel. The multipath propagation phenomenon is the result of environmental factors that influence the data signals as they travel between the base station and the mobile device, including, for example, ionospheric reflection and refraction, atmospheric ducting, reflection from terrestrial objects and reflection from bodies of water. Because of these factors, the data signals experience multipath interference that results in constructive interference, destructive interference, or fading, and phase shifting of the data signals.
The base stations and mobile devices of MIMO communications systems may each have multiple antennas, for example, configured as an antenna array or multiple radiating antenna elements configured on a single antenna. The term “advanced antenna” as used herein refers to both antenna arrays as well as single antennas with multiple radiating antenna elements, and refers to an integrated system in which each antenna (in an array) and radiating antenna element (for a single antenna) is individually logically controllable.
MIMO communications systems require testing. A typical MIMO test system for testing a device under test (DUT) includes an anechoic chamber, the DUT in the anechoic chamber, a test system computer, and various electrical cables for interconnecting components. During over the air (OTA) testing, the test system computer receives information from the DUT that the test system computer processes to evaluate the transmit and/or receive capabilities of the DUT as the DUT is subject to OTA testing. The OTA testing may involve an advanced antenna of the DUT and/or of a user equipment (UE) device or a UE device emulator, for example, communicating by selectively controlling the advanced antenna to form beams. A complex weight pattern is introduced to the advanced antenna in the time domain signal to form a beam. Beam characteristics are compared against expectations to measure whether the advanced antenna of the DUT works properly. Beam characteristics include, e.g., total transmit power, error vector magnitude (EVM) of modulation formats, antenna radiation pattern, etc.
The next generation of wireless infrastructure (e.g., base stations) and mobile devices will fall under the 5th generation (5G) standard(s) which are still being negotiated at the time of this application. Beamforming (i.e. generation of beams using advanced antennas) is a key aspect of 5G. The gain obtained by beamforming is needed to cope with the increased path loss of higher frequency bands as well as to increase the 5G systems capacity. The elements of an advanced antenna in 5G will be very small and there will be a large number of such elements integrated together with other electrical components on the same circuit board. For these reasons, conventional MIMO testing may not be feasible, or even possible, for 5G base stations and mobile devices.
As explained above, traditional OTA testing of a DUT is accomplished using an advanced antenna of multiple antennas or radiating antenna elements onto which a complex weight pattern is introduced to form a beam that is then applied to a time domain signal. The traditional methods are not amenable to applying different beams per subcarrier or CP-OFDM symbol since they are applied to the time domain signal. The traditional approaches cannot be directly applied to wired testing of the DUT because the beamforming effect is achieved due to the wireless signal propagation properties between, e.g., the advanced antennas in the OTA test system. Moreover, as the required radiation patterns of beams are narrower and the number of beams bigger, system cost and complexity increases, particularly if external equipment is added since testing requires increased synchronization as additional equipment is added. Analog beam simulation for wired device testing in CP-OFDM systems described herein provides for testing a DUT without adding additional equipment.